The present invention relates to a capacitor-discharge (CD) ignition system for two-stroke internal combustion engines. More particularly, the present invention is related to a CD ignition system which inhibits sustained engine operation in the event that the crankshaft is rotated in a reverse direction, that is, the direction opposite that contemplated by the engine design and associated mechanism connected to the crankshaft of the engine.
Due to the peculiar operation of a two-stroke internal combustion engine, it is possible to start the engine and to sustain engine operation with the crankshaft rotating in either a forward or a reverse direction. In this respect, the terms "forward" and "reverse" are utilized for convenience to differentiate between the two possible directions of crankshaft rotation. Normally, the engine is designed to operate in the "forward" direction and the ignition system is optimumly timed to fire the spark plug slightly in advance of the top dead center position of the piston and crankshaft. Since the plug fires in the vicinity of top dead center position, however, and because the two piston strokes of the engine cycle are carried out in the same manner regardless of which direction of the crankshaft is rotated, it is possible to have sustained engine operation for both forward and reverse crankshaft rotations.
CD ignition systems have anti-reverse features which prevent the engine from continuing to operate in the reverse direction already exist in the prior art. U.S. Pat. No. 3,554,179 issued Jan. 12, 1971 to the Assignee of the present invention discloses a CD ignition system in which a trigger signal energizing a silicon control rectifier is derived from a trigger coil excited by first flux-varying element carried on a flywheel of the engine. The first flux-varying element is positioned on the flywheel to discharge the capacitor and produce an ignition spark at an appropriate time during the enginge cycle, that is, in the vicinity of top dead center during forward rotation of the crankshaft. A second flux-varying element is almost mounted on the flywheel at a position circumferentially displaced from the first element and the second element discharges the capacitor and produces a spark when the crankshaft rotates in the reverse direction. The spark produced by the second element, however, is timed to occur during the engine cycle so far in advance of the top dead center position that sustained engine operation is inhibited.
While the use of two-flux varying elements is feasible in a CD ignition system to produce an anti-reverse feature, it has been discovered that the anti-reverse feature can also be derived from a system having only a single-flux varying element.
It is, accordingly, an object of the present invention to disclose a CD ignition system with an anti-reverse feature that requires only one flux-varying element to produce an appropriately timed spark for maintaining engine operation during forward crankshaft rotation and to discharge the capacitor without maintaining engine operation during reverse crankshaft rotation.